What knowest thou that we know not? - What pretensions or claims to wisdom have you which we have not? We have had, at least, equal advantages, and may be presumed to know as much as you.

What knowest thou - Is it likely that thy intellect is greater than ours; and that thou hast cultivated it better than we have done ours?
What understandest thou - Or, Dost thou understand any thing, and it is not with us? Show us any point of knowledge possessed by thyself, of which we are ignorant.

What knowest thou that we know not?.... Which are pretty near the words of Job to his friends, Job 12:3; and to the same sense is what follows:
what understandest thou which is not in us? in our hearts, minds, and understanding; or among us, which one or other, or all of us, have not: yet all men have not knowledge alike; some that profess themselves to be wise, and to have a large share of knowledge, are fools; and such who think they know something extraordinary, and more than others, know nothing as they ought to know; and such who have gifts of real knowledge have them different one from another; even of the things known there is not a like degree of knowledge, and particularly in spiritual things; some are little children in understanding, some are young men and know more, and some are fathers, and know most of all; an equality in knowledge belongs to another state, to the latter day glory, when the watchmen shall see eye to eye, and all shall know the Lord, from the least to the greatest, and especially to the ultimate glory, when saints will know as they are known.

in us--or, "with us," Hebraism for "we are aware of."